It is known that polymer and polymer-based membranes may be used in a wide variety of fluid separation processes, such as gas separation, desalination, removal of pathogens or other substances from liquids, such as water, and other applications requiring selective permeation, such as controlled atmosphere food packaging. In gas separations, for example, membranes can be used to separate air into oxygen-rich and nitrogen-rich streams. Gas separation membranes can also be used to remove carbon dioxide and other impurities from natural gas as well as selective removal of hydrogen from a wide variety of process streams important in the chemical, petrochemical, and other industries.
For many applications of membranes, including those mentioned above, the membranes are only commercially viable if they can be made very thin, in many cases on the order of less than about 10 μm or so in thickness. As membranes become thinner, the probability of developing selectivity-destroying pinhole defects in the membrane becomes higher.
Separation membranes can be prepared on large scale from solutions of polymers in a suitable solvent by methods widely known in the art. The polymers used in these applications, including, polysulfones, polyimides, poly(dimethyl siloxanes), polyethers, poly(vinylidene fluoride) and related materials, are typically only soluble in organic solvents. The solvents constitute the dominant mass in membrane processing and must be removed following membrane formation. These solvents, can be flammable and toxic. Additionally, these solvents are expensive not only to purchase but also to dispose of at the end of membrane processing. In many cases, solvent costs, including initial solvent purchases, solvent handling equipment, and solvent disposal equipment and processes are significant costs in the manufacturing of membranes for fluid separations. Therefore, there is a need in the membrane separation field to have methods to prepare membranes via solventless processes.